If you get lost or stranded in the wilderness, the one thing you'll need to live, above all else, is drinkable water. Humans just can't live without it. You might be able to live a few weeks without food, but without water you'll be lucky to last a few days. For this reason, you should bring along more than one way of purifying water on any trek into the wild.
Water filters are your best option and they come in all shapes, sizes and prices. Some are no bigger than a large drinking straw. Other pump models screw onto your water bottle and can filter up to 100 gallons (378 liters) without needing a new purification cartridge. These models work fast too, filtering about a quart of drinkable H2O in just a few minutes. Just to cover your bases, you should also pack some water filter tablets in your pack. They're typically iodine or chlorine pills that dissolve in water to make it OK to drink. The water may not taste great, but it'll keep you alive. Think ahead and pack the pills in different areas in case you become separated from your backpack. Keep the filter in your backpack and your tablets and emergency filter in a waist pack or even carry them on your person.